Magnetic pump

ABSTRACT

Disclosed is a magnetic pump such that it is possible to wirelessly monitor and control the operating state of a pump from a location separated from the pump. Specifically disclosed is a magnetic pump provided with a pump main body equipped with a pump case having an inlet and an outlet, and an impeller stored within the pump case in a rotatable manner and linked to a magnetic means, a rotating magnetic field generating means separated from the pump main body and for imparting a rotating magnetic field to the magnetic means; and a means for detecting the potential difference between the rotating magnetic field and the magnetic field produced by the magnetic means and imparted outward.

TECHNICAL FIELD

The present invention relates to a magnetic pump.

BACKGROUND ART

Extensive research has been conducted into pumps intended for variousapplications. Additionally, the development of new materials, as well asprogress in micro- and non-structure production technologies, have ledto the development of small-scale pumps of various types. However,substantially all of these small-scale pumps are controlled by anelectrical cable or battery.

In recent years, magnetic pumps provided with external magnetic fieldcontrol have been introduced in order to solve this problem (seeNon-patent Document 1). Magnetic pumps have attracted attention due totheir important role in pharmaceutical delivery and uTAS.

Pumps for medical applications are classified into three types accordingto operating mechanisms: centrifugal pumps, axial flow pumps, andpulsatile pumps. Blood pumps are further classified into two types:pulsed flow pumps and continuous flow (rotary) pumps.

Continuous flow (rotary) pumps have been developed for use as bloodpumps in recent years (see Patent Document 1, Non-patent Documents 2 to4). Pulsed flow pumps, being of valve design, are expensive and veryheavy, have low efficiency, are difficult so control, and have highpower consumption and low productivity, wherein continuous flow (rotary)pumps have various advantages. Continuous flow (rotary) pumps, lackingvalves, are inexpensive, small in scale, and lightweight, as well asbeing simple to control, and have low power consumption and highproductivity.

In a conventional continuous flow (rotary) pump, in cases in which theoperating state of the pump is to be monitored, it is necessary tofurnish the flow path with a pressure gauge or flow meter. This requiresplacing an extra device in proximity to the pump, as well as extrawiring for this purpose. Particularly in the case of a blood pump forimplantation in the body, this is a significant obstacle to practicalapplication.

CITATION LIST Patent Literature

Patent Document 1: JP 7-75667 A1

Non-Patent Literatures

Non-patent Document 1: A. Yamazaki, M. Sendoh, K. Ishiyama, K. I Arai,and T. Hayase (2003), IEEE Trans. on Magnetics, 39, 5

Non-patent Document 2: T. Yamane (2002), J. Artif. Organs, 5, 149-155

Non-patent Document 3: Jarvik, R. K. (1995), Artif. Organs, 19, 565-570

Non-patent Document 4: Masuzawa, T., Kita, T., Okada, Y. (2001), Artif.Organs, 25, 395-399

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to solve the problemsencountered in continuous flow (rotary) pumps of the prior art, andprovide a magnetic pump in which operating conditions of the pump bodycan be monitored and controlled wirelessly, from a location away fromthe pump body.

Solution to Problem

In order to solve the aforementioned problems, the present inventionprovides the following magnetic pump.

(1) A magnetic pump, provided with: a pump body provided with a pumpcasing having an inlet and an outlet, and an impeller rotatably housedwithin the pump casing, and linked to a magnetic means; a rotatingmagnetic field generating means separate from the pump body, and adaptedfor imparting a rotating magnetic field to the magnetic means; and meansfor detecting a phase difference between the rotating magnetic field anda magnetic field produced outward by the magnetic means.

(2) The magnetic pump according to (1), characterized in that the meansfor detecting a phase difference detects a phase difference between avoltage arising from rotation of the magnetic means and a voltagearising from the rotating magnetic field, and monitors an output of thepump on the basis of the phase difference.

(3) The magnetic pump according to (1) or (2), characterized in that themeans for detecting a phase difference includes a detection coil fordetecting the voltage arising from rotation of the rotating magneticfield and of the magnetic means; calculates the voltage arising fromrotation of the magnetic means, using the difference in a known voltagearising from rotation of the rotating magnetic field with respect to thevoltage detected by the detection coil; and detects the phase differencewith respect to the known voltage arising from the rotating magneticfield.

(4) The magnetic pump according to (3), characterized in that thedetection coil is furnished at a location away from the pump body.

(5) The magnetic pump according to any of (1) to (4), characterized inthat the rotating magnetic field generating means is a plurality offixed coils.

(6) The magnetic pump according to any of (1) to (5), characterized inthat the impeller is a multistate impeller.

(7) The magnetic pump according to any of (1) to (6), characterized inthat the pump is a blood pump.

(8) The magnetic pump according to any of (1) to (7), characterized inthat the magnetic means is a permanent magnet.

Advantageous Effects of Invention

The present invention makes possible a magnetic pump in which the pumpcan be driven wirelessly, and the operating conditions of the pump bodycan be monitored and controlled wirelessly, from a location distant fromthe pump body.

In particular, the magnetic pump according to the present inventionmakes a significant contribution to the practical application of a bloodpump for implantation in the body, which is required to be inexpensive,small in scale, and lightweight, as well as being simple to control, andhaving low power consumption.

BRIEF DESCRIPTION OF DRAWINGS

(FIG. 1) is a diagram showing generation of a rotating magnetic fieldand a driving method;

(FIG. 2) is a hodograph of inflow and outflow of an impeller;

(FIG. 3) is a diagram showing design and manufacture of a pump body;

(FIG. 4) is a diagram showing a flow dynamic simulation of a dischargepart;

(FIG. 5) is a diagram showing the relationship of flow rate andpressure;

(FIG. 6) is a photograph of an experimental setup;

(FIG. 7) is an exploded perspective view of a pump body;

(FIG. 8) shows a voltage waveform detected by a detector coil;

(FIG. 9) is a photograph of a right heart assist device forextracorporeal driving, as needed, during an animal experiment; and

(FIG. 10) shows time series curves of right heart assistive effectduring the animal experiment.

DESCRIPTION OF EMBODIMENTS

(Basic Principle of Operating Mechanism)

A magnetic pump is driven by a rotating magnetic field. Magnetic torqueis the essential energy supply. An NdFeB permanent magnet of the rotoris synchronized to a rotating magnetic field. The rotation velocityfluctuates, depending on the frequency of the magnetic field.

FIG. 1 shows the basic principle of a rotating magnetic field and thebasic principle of a synchronous state within a rotating magnetic field.As shown in FIG. 1 (a), in order to generate a uniform rotating magneticfield, the angle of intersection of a coil 1 and a coil 2 is set to 90°.It will be appreciated from FIG. 1 (b) that the phase difference of theinput current signals is 90°.

In this state, a rotating magnetic field is generated as the sum of thevectors shown in FIGS. 1 (c) and (d). The magnetic torque between therotating magnetic field and the magnetic moment of the NdFeB permanentmagnet can be represented as follows:

T=mH sin θ(Nm)  (1)

-   -   (m is the magnetic moment of the magnet, H is the rotating        magnetic field, and θ is the angle between m and H).

(Fundamental Theory of a Centrifugal Pump and an Impeller)

A centrifugal pump relies on the basic principles of angular momentumtheory and moment of momentum. Specifically, a centrifugal pump convertsenergy from kinetic energy to pressure energy. The amount of energyexerted on a liquid is proportional to the velocity at the edge or bladetip of the impeller. FIG. 2 shows the velocity at the edge or blade of asingle impeller. In FIG. 2, w is the relative velocity of particles of aliquid, v is the absolute velocity of particles of a liquid, u is theperipheral velocity, r is the radius, α is the angle between u and v,and β is the angle of the blade. The characteristics of an impeller anda pump vary depending on the blade shape, which is determined by theblade angle β₂.

According to angular momentum theory, torque T_(torque) and powerP_(power) can be represented as follows:

$\begin{matrix}{T_{torque} = {\rho \; Q\mspace{14mu} \left( {{r_{2}v_{2}\mspace{14mu} \cos \; \alpha_{2}} - {r_{1}v_{1}\mspace{14mu} \cos \; \alpha_{1}}} \right)}} & (2) \\\begin{matrix}{P_{power} = {T_{torque} \times \omega}} \\{= {\rho \; {gQH}_{p}}} \\{= {\rho \; Q\mspace{14mu} \left( {{u_{2}v_{2}\mspace{14mu} \cos \; \alpha_{2}} - {u_{1}v_{1}\mspace{14mu} \cos \; \alpha_{1}}} \right)}}\end{matrix} & (3)\end{matrix}$

In the aforementioned equations, o is the fluid density, Q is thequantity of flowing liquid, H_(p) is the pump head, g is gravity, and ωis the angular velocity.

For the purpose of acquiring the actual pump head, an angle (α₁=90°) isassumed. In this case, the pump head (H_(p)) can be represented asfollows:

H_(p)=1/g u₂v₂ cos α₂  (4)

In order to analyze the effect of the blade angle (β₂), equation (4) istransformed by β₂, and then α₂ is transformed by V_(2u) as shown in FIG.2. The pump head (H_(p)) can be rewritten as follows:

H _(p)=1/g (u ₂ ² −u ₂ v _(n2) cot β₂)  (5)

At constant rotation speed, the pump head fluctuates depending on theangle (β₂), in accordance with the following three preconditions.

1. β₂>90°: when cot β₂<0 and v_(n2) cot β₂<0, the head increases inaccordance with decreasing flow rate.

2. β₂=90°: when cot β₂=0 and v_(n2) cot β₂=0, the head is a constantvalue, irrespective of the flow rate.

3. β₂<90°: when cot β₂>0 and v_(n2) cot β₂>0, the head decreases inaccordance with increasing flow rate.

(Design and Fundamental Characteristics of Pump Body)

The pump body of the magnetic pump according to the present inventionincludes a multistate impeller and an NdFeB permanent magnetic(diameter: 18.8 mm, thickness: 4 mm). Because the impeller is offloating design, the pump casing requires no rotating shaft or bearing.Common mechanical problems are eliminated thereby. A magnetic pump has anumber of advantages in medical applications. These include a simplerconstruction with no mechanical problems, by virtue of a wireless designwithout the need for a battery; and the fact that no heat whatsoever isgenerated. The fundamental characteristics of a magnetic pump varydepending on the magnetic field and the operating frequency.

The intersection point and magnetic field density of two coils determinethe distance between the pump body and the drive coils. The dischargepressure can be adjusted at this time, through the frequency. In thecase of a vibrating flow pump, pressure fluctuates depending on theresonance frequency. In a centrifugal pump, however, up to thesaturation point, pressure is proportional to operating frequency. Thepump body of the present invention can rotate in either of twodirections, in accordance with the rotation direction of the rotatingmagnetic field (counterclockwise or clockwise). The flow rate andpressure in this case will be determined by equation (5). When therotation direction is counterclockwise, the blade angle (β₂) formed onthe impeller is less than 90°. However, when the rotation direction isclockwise, the blade angle (β₂) is greater than 90°.

FIG. 3 shows the assembled impeller and pump body. In FIG. 3, (a) showsthe impeller in 3D, (b) shows a multistage impeller provided with a disktype NdFeB permanent magnetic constituting the rotor, and (c) shows thecompletely installed pump body, respectively.

Measured values of a single impeller were taken at 1 mm, with a 0.2 mmgap between the rotor and the inner wall of the pump casing. Because therotor is of floating design, this space is important in terms ofdetermining starting torque. The flow rate and the dynamic pressure aredetermined by the diameter of the discharge part. For example, with asmaller diameter, it is possible to increase the dynamic pressure, butthe flow rate will drop at a constant rpm value.

FIG. 4 is a drawing showing a flow dynamic simulation of the dischargepart of the pump casing. In FIG. 4, (a) shows the pressure distributionacross the diameter (6 mm and 3 mm) of the discharge part, and (b) showspressure measurement results (dynamic pressure, static pressure, andtotal pressure: discharge part 6 mm), respectively. An optimal size ofthe discharge part can be designed through flow dynamic simulations.

(Experimental Results)

The inventors fabricated a magnetic pump. The design thereof comprised apump body, drive coils, and a power supply. As mentioned previously, thedistance between the pump body and the drive coils is determined by theangle at the intersection point of the drive coils.

This experiment was carried out with the angle at the intersection pointof the drive coils set to 90°. The phase difference of the currentsignals of the two drive coils was fixed at 90°. The operating frequencyfor driving the magnetic rotor was 10 Hz to 100 Hz (rpm: ≦6,000 rpm).For this experiment, two types of pump casing (having outflow diameterof 3 mm and 6 mm), and tubes of 6 mm, 8 mm, and 10 mm, where employed.The characteristics of the magnet (size, magnetic moment) on the rotorare important factors within the rotating magnetic field, as thesegenerate the torque.

FIG. 5 (b) to (d) show various characteristics of the magnetic pump. InFIG. 5, (a) shows a test bed for circulation purposes, (b) shows acomparison of discharge parts (6 mm and 3 mm diameter), (c) shows therelationship of flow rate and pressure (for a 6 mm discharge part and a10 mm output tube), and (d) shows change in flow rate at increasingfrequencies, respectively.

Firstly, the relationship of flow rate and pressure is an inverselyproportional relationship.

Secondly, flow rate and pressure are proportional to operating frequency(rpm).

However, the impedance on the coils fluctuates depending on thefrequency. Ultimately, increase of the operating frequency gives rise toa decline in the driving current. Finally, the flow rate and pressureare determined by the size of the discharge part, together with theoperating frequency. Flow rate and pressure were compared for dischargeparts of 3 mm and 6 mm. In this case, the pressure difference was 400Pa, and as shown in FIG. 5 (b), when the output tube diameter was 6 mm,the flow rate was 500 mL/min at 70 Hz. However, as shown in FIG. 5 (c),with a 6 mm discharge part and a 10 mm output tube, while the flow ratewas high (3,200 mL/min at 70 Hz and 4,800 mL/min at 100 Hz), thepressure declined to a maximum of 200 Pa.

(Monitoring the Operating State)

The procedure for monitoring the operating state of the magnetic pumpaccording to the present invention is described.

During operation of the magnetic pump, two types of magnetic field existin proximity to the detection coil. Specifically, these are the rotatingmagnetic field produced outward due to rotation of the built-in magnetserving as the magnetic means, and the magnetic field generated by thebuilt-in magnet.

During this process, the magnetic field that is produced outward by themagnet in association with rotation of the built-in magnet rotates aswell, and therefore by disposing the detection coil at an appropriatelocation, induced electromotive force arises in the coil, andalternating current voltage proportional to the rotation frequency andthe magnetic field intensity is generated at both ends of the coil.Rotation of the built-in magnet can then be monitored from the voltagewaveform at both ends of the detection coil.

The detection coil is placed at a location where it can efficientlydetect the magnetic field generated by the built-in magnet, and at thesame time, detects the rotating magnetic field exerted from the outsideas well. However, there is a phase difference between these two magneticfields, and measurement of this phase difference in and of itselfconstitutes important information for ascertaining the rotation behaviorof the built-in magnet.

The pump operates as a pump by virtue of imparting force on a nearbyfluid. This is equivalent to the load on the motor. From the basicprinciple of magnetic torque, the torque and the angle difference of theorientation of the magnetic field exerted from the outside and of themagnetization of the magnet are proportional, and therefore, in the caseof this pump, the magnet always has somewhat of a phase lag with respectto the rotating magnetic field, while rotating at the same rotationspeed. The quantity of this phase lag is proportional to the magnitudeof the torque acting between the rotating magnetic field and the magnet,and this is specifically proportional to the output torque of the pump.

The extent of the phase lag at which the built-in magnet rotates withrespect to the rotating magnetic field may be detected from the phasedifference of the rotating magnetic field and the magnetic fieldproduced outward by the built-in magnet. Where two magnetic fields areobserved simultaneously by a single detection coil, because the phase ofthe external rotating magnetic field is known, the phase difference ofthe rotating magnetic field and the built-in magnet can be ascertained.

The torque can then be calculated on the basis of this phase difference,so that the pump output can be monitored. Specifically, the phasedifference is larger in the case of higher pump output, whereas thephase difference is smaller is the case of lower pump output. Inspecific terms, when the phase difference is zero, the term θ in theaforementioned equation (1) is zero and toque becomes zero; this isequivalent to a case of rotation at no load (zero output). The phasechanges in association with increasing load (increasing output), withthe torque reaching the maximum in the case of a 90 degree phase, atwhich point the output reaches the maximum output of the pump.Accordingly, the instantaneous output ratio with respect to the maximumoutput of the pump can be monitored in real time, through phasemeasurement.

Naturally, the detection coil is disposed at a location away from thepump body.

For example, where the pump is employed in an artificial heartapplication, the detection coil would be disposed outside the body, sothat the operation of the pump body inside the body can be monitored.Employing this basic principle, it is possible to build a so-calledfeedback system in which, in the event that of a sudden change to a highload, for example, the intensity of the external rotating magnetic fieldincreases immediately to compensate.

(Experimental Demonstration of Basic Principle)

In order to experimentally demonstrate the aforementioned basicprinciple, a detection coil was closely attached about the pump casing,and an external rotating magnetic field was applied to the pump by twointersecting coils while observing the output voltage of the detectioncoil. FIG. 6 shows a photograph of the experimental setup. FIG. 7 is anexploded perspective view of the pump body. The detection coil has beenarranged on the surface of the pump casing.

FIG. 8 shows the voltage waveform detected by the detector coil, as asolid line. Because the detector coil simultaneously measures twomagnetic fields, the waveform shown by the solid line in FIG. 8 isobserved.

Meanwhile, because the external rotating magnetic field is known, thewaveform shown by the broken line can be prepared in advance. Thevoltage waveform arising from rotation of the built-in magnet, shown bythe single dot-and-dash line, can then be calculated from the differentof these two waveforms.

Thereafter, measuring the phase difference of the two waveforms shown bythe broken line and the single dot-and-dash line gives the pump output.In FIG. 8, the broken line reaches maximum of 90 degrees, whereas thesingle dot-and-dash line reaches maximum at 60 degrees, leading to theexistence of a phase difference of 30 degrees. As the load changes, thephase difference changes as well, bringing about parallel movement ofthe single dot-and-dash line to left or right in the drawing.

(Animal Experiment)

An animal experiment was carried out in order to experimentallydemonstrate the effect of the magnetic pump of the present invention.

FIG. 9 is a photograph of a right heart assist device for extracorporealdriving, as needed, during an animal experiment. A bypass circuitleading from the right ventricle to the pulmonary artery is implanted,and a permanent magnet joined to an impeller is employed to generatedrive force. The impeller for subcutaneous implantation has beeninstalled within the bypass circuit from the right ventricle to thepulmonary artery. Because this bypass circuit is subcutaneouslyimplanted thereafter, full, sterile implantation is achieved.

FIG. 10 shows time series curves of right heart assistive effect in theanimal experiment, by the assisted circulation device which can bedriven from outside the body. From the top, pump outflow-side pressure,inflow-side pressure, and pump flow rate are shown. It will beappreciated that once driving was initiated, the pump flow rateincreased, representing right heart assistive effect.

While this animal experiment was carried out to assist the right heart,the device can be implemented to assist left heart as well.

While the present invention has been described herein taking the exampleof a blood pump, the present invention is not limited to the blood pumpcited herein by way of an embodiment, and can be applied in all mannerof magnetic pumps.

The present invention is implementable, for example, in a case in whicha pump body placed to the other side of a wall is to be driven from thenear side of the wall.

Specifically, this would be particularly effective in cases in which itis undesirable to place the drive source to the other side of a wall,such as when the other side of the wall is in a high-temperature,low-temperature, vacuum, or highly radioactive state, or in a sterilestate.

The present invention is moreover effective in a case in which a pumpbody disposed in a confined site such as in a tube or pipe is to bedriven from the outside.

1-8. (canceled) 9: A magnetic pump, providing with: a pump body providedwith a pump casing having an inlet and an outlet, and an impellerrotatably housed within the pump casing, and linked a magnet; a rotatingmagnetic field generator separated as a discrete element from the pumpbody, and adapted for imparting a rotating magnetic field to the magnet;and a detector for detecting a phase different between said rotatingmagnetic field and a magnetic field produced outward by said magnet;wherein the detector for detecting a phase difference simultaneouslydetects a voltage arising from rotation of said magnet and a voltagearising from said rotating magnetic field; detects the phase differencethereof utilizing a known voltage arising from the rotating magneticfield; and monitors the output of the pump on the basis of the phasedifference. 10: The magnetic pump according to claim 9, wherein saiddetector for detecting a phase difference includes a detection coil fordetecting the voltage arising from rotation of said rotating magneticfield and of said magnet; calculates the voltage arising from rotationof said magnet using the difference in a known voltage arising fromrotation of the rotating magnetic field, with respect to the voltagedetected by the detection coil; and detects the phase difference withrespect to the known voltage arising from the rotating magnetic field.11: The magnetic pump according to claim 10, wherein the detection coilis furnished at a location away from the pump body. 12: The magneticpump recording to claim 9, wherein said rotating magnetic fieldgenerator comprises a plurality of fixed coils. 13: The magnetic-pumpaccording to claim 10, wherein said rotating magnetic field generatorcomprises a plurality of fixed coils. 14: The magnetic pump according toclaim 11, wherein said rotating magnetic field generator comprises aplurality of fixed coils. 15: The magnetic pump according to claim 9,wherein said impeller comprises a multistage impeller. 16: The magneticpump according to claim 10, wherein said impeller comprises a multistageimpeller. 17: The magnetic pump according to claim 11, wherein saidimpeller comprises a multistage impeller.
 18. The magnetic pompaccording to claim 12, wherein said impeller comprises a multistageimpeller. 19: The magnetic pump according to claim 9, wherein said pumpcomprises a blood pump. 20: The magnetic pump according to claim 10,wherein said pump comprises a blood pump. 21: The magnetic pumpaccording to claim 11, wherein said pump comprises a blood pump. 22: Themagnetic pump according to claim 12, wherein said pump comprises a bloodpump. 23: The magnetic pump according to claim 13, wherein said pumpcomprises a blood pump. 24: The magnetic pump according to claim 14,wherein said pump comprises a blood pump. 25: The magnetic pumpaccording to claim 9, wherein said magnet comprises a permanent magnet.26: The magnetic pump according to claim 10, wherein said magnetcomprises a permanent magnet. 27: The magnetic pump according to claim11, wherein said magnet comprises a permanent magnet. 28: The magneticpump according to claim 12, wherein said magnet comprises a permanentmagnet. 29: The magnetic pump according to claim 13, wherein said magnetcomprises a permanent magnet. 30: The magnetic pump according to claim14, wherein said magnet comprises a permanent magnet. 31: The magneticpump according to claim 18, wherein said magnet comprises a permanentmagnet.